This invention relates to a pilot operated pressure and vacuum relief valve for use with hydraulically controlled valves by disposing said pilot valve in the actuator ports of said hydraulically controlled valves.
Such a valve may be regarded as a combined pressure and vacuum relief valve since it is usually so connected in a fluid pressure system that its opening effects communication of the system with a reservoir or other source of fluid which is unpressurized or at atmospheric pressure. Thus, when system pressures are excessively high, the valve allows fluid from the system to flow to the reservoir or drain, and when the pressure of fluid in the system falls below that of fluid in the reservoir, the valve likewise opens to permit fluid from the reservoir to flow into the system. This kind of valve is disclosed in U.S. Pat. Nos. such as 2,989,072 to Banker and 3,100,503 to Tennis and also disclosed in Japanese patent publication Nos. 36-2635 and 38-1911.